Two oil companies working to develop what they say will be a big new oil field in the Colville River Delta area announced Tuesday that they are shifting their ownership split in the project.

But a decision to put off drilling this winter means about 500 contract Slope workers won't be hired.

Repsol, a Spanish energy company, and privately held, Denver-based Armstrong Oil and Gas Inc. have agreed to "strategically re-align their interests in their Alaska North Slope exploration and development venture," Armstrong said in a statement.

The resulting deal, worth more than $800 million, will give Armstrong majority ownership in both the development area and the exploration area where the companies have drilled 16 wildcat and appraisal wells in the past four years, the statement said.

Under the deal, Armstrong's share will ultimately be boosted from 30 percent to 45 percent in the development area and to 75 percent in the exploration area. Armstrong also purchased an option on an additional 6 percent of the development area, which -- when exercised -- would give it a 51 percent share and make it the operator.

Jan Sieving, Repsol's North America vice president for public affairs, said the companies are working together on transition plans. Those transitions "will determine the impact to the 20 employees and 20 contractors currently working in Repsol's Anchorage office," she said. "Repsol will try to place impacted Alaska project employees elsewhere in the company."

She also said that the decision to put off drilling this winter means the company won't be hiring about 500 contract Slope workers, as it has in past winter exploration seasons.

The 2015-16 exploration program would have included up to three drill sites, about 40 miles of ice road and an airstrip and central camp placed on ice, according to the operations plan submitted last month by Repsol to the Alaska Department of Natural Resources.

Armstrong has been doing business in this Alaska project as 70 & 148 LLC and GM Exploration Co. LLC.

Further review will determine whether those are considered proven, probable or possible reserves, the statement said.

If developed, the project could result in production of about 120,000 barrels per day, the statement said.

The development project is called Nanushuk, Sieving said.

The companies' progress represents new success for the North Slope, Armstrong's president said in the statement.

"Armstrong and Repsol's North Slope project is representative of the new movement in Alaska where smaller independents work and operate in areas previously dominated by major oil companies," Bill Armstrong, president of the Denver-based company, said in the statement.